Block copolymers of polydimethylsiloxane polymers based solely on polydimethyl-siloxane lack tensile strength. Consequently, several references suggest ways for conveniently increasing the strength of these siloxane polymer elastomers. For example, various references suggest that mechanical properties of polysiloxane polymers can be improved substantially through the preparation of block copolymers which include as a repeating unit a "soft" polysiloxane block or segment and any of a variety of other "hard" blocks or segments such as polyurethane. See, for example, (Ward) U.K. Patent GB 2 140 444B, published Jun. 5, 1985, (Cavezzan et al) U.S. Pat. No. 4,518,758, (Nyilas) U.S. Pat. No. 3,562,352, and (Kira) U.S. Pat. No. 4,528,343.
Segmented polydimethylsiloxane polyurea elastomers, with silicone segment molecular weights less than about 4,000, prepared from silicone diamines and diisocyanates are described in Polymer, Vol. 25, pages 1800-1816, December, 1984. This reference reveals that synthesis of higher molecular weight silicone segments could not be achieved by the disclosed method. This process also leads to significant amounts of monofunctional and non-functional silicone contaminants. These contaminants remain in the polyurea elastomers prepared from such diamines.